linux-kernel - [PATCH] scripts/faddr2line: Only use text symbols to calculate function size

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Message-Id: <2fb2bc4e857848c83cfa96483e4b25b23d46be49.1651516951.git.jpoimboe@redhat.com>
Date:   Mon,  2 May 2022 11:43:50 -0700
From:   Josh Poimboeuf <jpoimboe@...hat.com>
To:     Peter Zijlstra <peterz@...radead.org>
Cc:     linux-kernel@...r.kernel.org,
        Kaiwan N Billimoria <kaiwan.billimoria@...il.com>
Subject: [PATCH] scripts/faddr2line: Only use text symbols to calculate function size

With the following commit

  efdb4167e676 ("scripts/faddr2line: Fix "size mismatch" error")

it was discovered that faddr2line can't just read a function's ELF
size, because that wouldn't match the kallsyms function size which is
printed in the stack trace.  The kallsyms size includes any padding
after the function, whereas the ELF size does not.

So faddr2line has to manually calculate the size of a function similar
to how kallsyms does.  It does so by starting with a sorted list of
symbols and subtracting the function address from the subsequent
symbol's address.

That calculation is broken in the case where the function is the last
(or only) symbol in the .text section, which can occur quite commonly in
a kernel module or a .o file.  In that case, the next symbol in the
sorted list might actually be a data symbol, which breaks the function
size detection:

  $ scripts/faddr2line sound/soundcore.ko sound_devnode+0x5/0x35
  bad symbol size: base: 0x0000000000000000 end: 0x0000000000000000

Fix it by only including text symbols in the symbol list.

Fixes: efdb4167e676 ("scripts/faddr2line: Fix "size mismatch" error")
Reported-by: Kaiwan N Billimoria <kaiwan.billimoria@...il.com>
Signed-off-by: Josh Poimboeuf <jpoimboe@...hat.com>
---
 scripts/faddr2line | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/scripts/faddr2line b/scripts/faddr2line
index 6c6439f69a72..2a130134f1e6 100755
--- a/scripts/faddr2line
+++ b/scripts/faddr2line
@@ -189,7 +189,7 @@ __faddr2line() {

 		DONE=1

-	done < <(${NM} -n $objfile | awk -v fn=$func -v end=$file_end '$3 == fn { found=1; line=$0; start=$1; next } found == 1 { found=0; print line, "0x"$1 } END {if (found == 1) print line, end; }')
+	done < <(${NM} -n $objfile | awk -v fn=$func -v end=$file_end '$2 !~ /[Tt]/ {next} $3 == fn { found=1; line=$0; start=$1; next } found == 1 { found=0; print line, "0x"$1 } END {if (found == 1) print line, end; }')
 }

 [[ $# -lt 2 ]] && usage
-- 
2.34.1